Epidermal Langerhans cells (LCs) function as the antigen-presenting cells in such cutaneous cell-mediated immune responses as contact hypersensitivity and in the mixed epidermal cell-lymphocyte reaction. They have also been implicated in the immune response in skin allograft rejection. Since organ culture of thyroid and pancreas has been shown to prolong allograft survival, presumably through the loss of antigen-presenting cells, we examined the effect of skin explant culture on LC survival. Human skin explants were placed in organ culture and examined serially as whole mouths of epidermis for the presence of LCs as judged by ATPase activity, and OKT-6 and HLA-DR antigens. Although we observed morphologic changes and an absolute reduction in the number of positively stained cells, culture for up to 28 days failed to deplete explants of these cells. Langerhans cells were also sought in the epidermal outgrowths that develop peripheral to the original explants. They were never seen in the area beyond 0.3 mm from the explant edge. Organ culture of skin thus provides a means to explore the contribution of LCs to skin allograft rejection by comparing the immunogenicity of epidermal portions of the explant with the epidermal outgrowth.